1. Field of the Invention
The present invention relates to a display device for complex transmission reflection characteristics and, more particularly, to a display device for complex transmission reflection characteristics, which displays a coordinate system, such as an impedance coordinate system or an admittance coordinate system used for measuring impedance or admittance of an RF circuit, individually or in a superposed manner.
2. Description of the Known Art
Smith charts, as shown in FIGS. 2(A) and 3(A), are conventionally used for analysis of RF circuits. A Smith chart was first used by Smith at the Bell Institute (U.S.A.) in the 1930s and is divided into an impedance chart shown in FIG. 2(A) and an admittance chart shown in FIG. 3(A).
An impedance chart is obtained by plotting impedance Z, expressed as complex number Z=R+jX which consists of resistance R and reactance X, using a frequency as a parameter. An admittance chart is obtained by plotting admittance Y, expressed as complex number Y=G+iB which consists of conductance G and susceptance B, using a frequency as a parameter.
Each of the impedance and admittance planes shown in FIGS. 2(A) and 3(A) can be superposed with a reflection coefficient plane. Note that a reflection coefficient plane represents a vector of reflection coefficient .GAMMA. given by .GAMMA.=.vertline..GAMMA..vertline.ej.theta. where .vertline..GAMMA..vertline. is the magnitude of a vector when the radius of the outermost circle of the Smith chart is 1, and .theta. is the rotational angle of the vector.
In conventional display devices which display polar coordinates or reflection characteristics in order to provide transmission characteristics represented in complex numbers, display methods of impedance or admittance coordinates are roughly divided into the following two systems:
According to the first system, a transparent plate with a polar chart, shown in FIG. 4, printed thereon is provided on the screen of a CRT. For monitoring, a transparent sheet made of cellophane or the like with the impedance chart shown in FIGS. 2(A), 2(B), and 2(C), or a polar chart shown in FIG. 4, printed thereon, is adhered to the transparent plate. In this manner, when obtained data is to be recorded, a semi-transparent recording sheet with the impedance chart shown in FIGS. 2(A), 2(B), and 2(C), or the polar chart shown in FIG. 4, printed thereon, is adhered to the screen of the CRT, and the displayed data is manually transferred to the recording sheet, using a soft pen or the like.
According to the second system, the polar chart shown in FIG. 4, or only the two impedance charts, shown in FIGS. 2(A) and 2(B), are separately, electronically displayed on the screen of the CRT.
With the first system, however, the transparent sheet may be misaligned with the transparent plate, or defective gain control may occur between the printed chart circle and the CRT, resulting in incorrect trace data. In addition, the data can only be recorded manually by the person monitoring the screen.
With the second system, since the compression impedance chart shown in FIG. 2(C) is not provided, the trace within a negative resistance region of .GAMMA.&gt;1 cannot be observed. In addition, unless the data is subjected to transformation of coordinates through 180.degree., the trace data of the admittance cannot be obtained. Since a constant conductance circle and a constant susceptance circle are not provided in the coordinate representation, a shift of the parameter in the admittance plane cannot be easily simulated.